Tunable green to red upconversion fluorescence of water-soluble hexagonal-phase core-shell CaF2@NaYF4 nanocrystals

Hexagonal NaYF4 nanocrystals (NCs) have been prepared by core-mediated hetero-shell growth process using polyvinylpyrrolidone (PVP) as chelating agents and cubic CaF2 as core. It is found that the NaYF4 NCs prepared by this strategy have narrow size distribution, small particle size and well water-soluble property, can be easily dispersed in water. Besides, by increasing the doping concentration of Tm3+ ions in Er3+-Yb3+ codoping system, the upconversion (UC) liminescence of CaF2@NaYF4: Yb/Er/Tm NCs was modulated from green to red by the naked eye. These NCs with red upconversion luminescence (UCL) and good water solubility show potential applications in biological labeling eld. (C)2015 Optical Society of America